
#include "md5.h"
#include <string.h>

#define LEFTROTATE(x, c) (((x) << (c)) | ((x) >> (32 - (c))))

static const uint32_t k[] = {
    0xd76aa478, 0xe8c7b756, 0x242070db, 0xc1bdceee,
    0xf57c0faf, 0x4787c62a, 0xa8304613, 0xfd469501,
    0x698098d8, 0x8b44f7af, 0xffff5bb1, 0x895cd7be,
    0x6b901122, 0xfd987193, 0xa679438e, 0x49b40821,
    0xf61e2562, 0xc040b340, 0x265e5a51, 0xe9b6c7aa,
    0xd62f105d, 0x02441453, 0xd8a1e681, 0xe7d3fbc8,
    0x21e1cde6, 0xc33707d6, 0xf4d50d87, 0x455a14ed,
    0xa9e3e905, 0xfcefa3f8, 0x676f02d9, 0x8d2a4c8a,
    0xfffa3942, 0x8771f681, 0x6d9d6122, 0xfde5380c,
    0xa4beea44, 0x4bdecfa9, 0xf6bb4b60, 0xbebfbc70,
    0x289b7ec6, 0xeaa127fa, 0xd4ef3085, 0x04881d05,
    0xd9d4d039, 0xe6db99e5, 0x1fa27cf8, 0xc4ac5665,
    0xf4292244, 0x432aff97, 0xab9423a7, 0xfc93a039,
    0x655b59c3, 0x8f0ccc92, 0xffeff47d, 0x85845dd1,
    0x6fa87e4f, 0xfe2ce6e0, 0xa3014314, 0x4e0811a1,
    0xf7537e82, 0xbd3af235, 0x2ad7d2bb, 0xeb86d391
};
static const uint32_t r[] = {
    7,12,17,22, 7,12,17,22, 7,12,17,22, 7,12,17,22,
    5,9,14,20, 5,9,14,20, 5,9,14,20, 5,9,14,20,
    4,11,16,23, 4,11,16,23, 4,11,16,23, 4,11,16,23,
    6,10,15,21, 6,10,15,21, 6,10,15,21, 6,10,15,21
};

void MD5_Init(MD5_CTX *ctx) {
    ctx->h0 = 0x67452301;
    ctx->h1 = 0xefcdab89;
    ctx->h2 = 0x98badcfe;
    ctx->h3 = 0x10325476;
    ctx->datalen = 0;
    ctx->bitlen = 0;
}

static void md5_transform(MD5_CTX *ctx, const uint8_t data[]) {
    uint32_t a = ctx->h0, b = ctx->h1, c = ctx->h2, d = ctx->h3, f, g, temp;
    uint32_t m[16];
    for (int i = 0; i < 16; ++i)
        m[i] = ((uint32_t)data[i*4]) | (((uint32_t)data[i*4+1]) << 8) |
               (((uint32_t)data[i*4+2]) << 16) | (((uint32_t)data[i*4+3]) << 24);
    for (int i = 0; i < 64; ++i) {
        if (i < 16) {
            f = (b & c) | ((~b) & d);
            g = i;
        } else if (i < 32) {
            f = (d & b) | ((~d) & c);
            g = (5*i + 1) % 16;
        } else if (i < 48) {
            f = b ^ c ^ d;
            g = (3*i + 5) % 16;
        } else {
            f = c ^ (b | (~d));
            g = (7*i) % 16;
        }
        temp = d;
        d = c;
        c = b;
        b = b + LEFTROTATE((a + f + k[i] + m[g]), r[i]);
        a = temp;
    }
    ctx->h0 += a;
    ctx->h1 += b;
    ctx->h2 += c;
    ctx->h3 += d;
}

void MD5_Update(MD5_CTX *ctx, const uint8_t *data, uint32_t len) {
    for (uint32_t i = 0; i < len; ++i) {
        ctx->buffer[ctx->datalen] = data[i];
        ctx->datalen++;
        if (ctx->datalen == 64) {
            md5_transform(ctx, ctx->buffer);
            ctx->bitlen += 512;
            ctx->datalen = 0;
        }
    }
}

void MD5_Final(uint8_t *digest, MD5_CTX *ctx) {
    uint32_t i = ctx->datalen;
    // Pad whatever data is left in the buffer.
    if (ctx->datalen < 56) {
        ctx->buffer[i++] = 0x80;
        while (i < 56)
            ctx->buffer[i++] = 0x00;
    } else {
        ctx->buffer[i++] = 0x80;
        while (i < 64)
            ctx->buffer[i++] = 0x00;
        md5_transform(ctx, ctx->buffer);
        memset(ctx->buffer, 0, 56);
    }
    // Append to the padding the total message's length in bits and transform.
    uint64_t bits = ctx->bitlen + ctx->datalen * 8;
    for (int j = 0; j < 8; ++j)
        ctx->buffer[56 + j] = (uint8_t)((bits >> (8 * j)) & 0xFF);
    md5_transform(ctx, ctx->buffer);
    // Output
    memcpy(digest, &ctx->h0, 4);
    memcpy(digest+4, &ctx->h1, 4);
    memcpy(digest+8, &ctx->h2, 4);
    memcpy(digest+12, &ctx->h3, 4);
}
